This invention relates to photodiodes for detecting far-uv radiation.
Far-uv radiation (wavelengths of less than 200 nanometers) has conventionally been detected using evacuated photodiodes. Examples of evacuated photodiodes are disclosed in Canfield et al., "NBS Detector Standards for the Far Ultraviolet", Applied Optics, vol. 12, pp. 1611-17 (July 1973). In one such vacuum photodiode (FIG. 2 of Canfield et al.), the ultraviolet radiation enters an evacuated chamber through a magnesium fluoride window, passes through the center of an anode ring surrounding the window, crosses the evacuated chamber, and strikes a photocathode (rubidium telluride or cesium telluride). The electrons emitted by the photocathode pass back across the evacuated chamber to the anode ring, creating a current that is measured externally. Canfield et al. also discloses windowless photodiodes, but these, too, are operated in a vacuum. A text on detectors authored by Sampson and published by Wiley in about 1965 discusses (section 7.3, pp. 224-244) photoelectron emmission generally, and describes evacuated photodiodes.